Fresh and clean air is essential for human health. Science and technology has promoted economical development. However, the exhausts of vehicles and factories, especially motor vehicles and heavy industry factories, seriously pollute the air.
The emission standard of motor vehicles has been increased persistently. However, the continuously increasing motor vehicles still brings about more and more serious air pollution. In a motor vehicle, the engine thereof burns fuel and converts chemical energy into mechanical energy. The burning process of fuel generates the polluting constituents, including nitrogen oxides (NOx), carbon monoxide (CO), hydrocarbons (HCs), and particulate matter (PM), which would form photochemical smog, deplete ozone, enhance the greenhouse effect, cause acid rain, damage the ecological environment and finally danger human health.
Carbon monoxide comes from incomplete combustion. The capability of carbon monoxide to combine with hemoglobin to form carboxyhemoglobin (COHb) is 300 times higher than the capability of oxygen to combine with hemoglobin to form oxyhemoglobin (HbO2). Therefore, too high a concentration of carbon monoxide would degrade the capability of hemoglobin to transport oxygen. Nitrogen oxides are generated by the combination of nitrogen and oxygen and mainly in form of nitrogen monoxide (NO) and nitrogen dioxide (NO2). Reaction of nitrogen oxides and hydrocarbons is induced by ultraviolet ray, generating poisonous photochemical smog, which has a special odor, irritates eyes, harm plants, and reduces the visibility of the ambient air. Nitrogen oxides can react with water in the air to form nitric acid and nitrous acid, which are the constituents of acid rain. Hydrocarbons can irritate the respiratory system even at lower concentration and will affect the central nervous system at higher concentration. Particulate matter can danger human health and can even cause cancer.
Therefore, many nations, including EU, USA, Japan and Taiwan, have regulated stricter emission standards for nitrogen oxides, carbon monoxide, hydrocarbons and particulate matter, such as BINS of USA and EURO 6 of EU, which not only regulate the emissions of the polluting constituents but also encourage the manufacturers to develop, fabricate or adopt the newest pollution control technologies and apparatuses.
A U.S. Pat. No. 5,401,372 disclosed an “Electrochemical Catalytic Reduction Cell for the Reduction of NOx in an O2-Containing Exhaust Emission”, which is dedicated to removing nitrogen oxides, wherein an electrochemical-catalytic reducing reaction and a vanadium pentaoxide (V2O5) catalyst convert nitrogen oxides into nitrogen. However, the prior art needs an electric source to power an electrochemical cell. Therefore, the prior art consumes power and cannot eliminate other polluting constituents simultaneously.
A U.S. patent application Ser. No. 13/362,247 disclosed an “Electrocatalytic Tube of Electrochemical-Catalytic Converter for Exhaust Emissions Control”, which can eliminate nitrogen oxides (NOx), carbon monoxide (CO), hydrocarbons (HCs), and particulate matter (PM) in the exhaust, and which comprises the electrocatalytic tubes that can be assembled to form a honeycomb monolith to be an advanced electrochemical-catalytic converter, wherein the nitrogen oxides are decomposed into nitrogen and oxygen, and wherein carbon monoxide, hydrocarbons, and particulate matter are oxidized into water and carbon dioxide. Therefore, the prior art can eliminate multiple polluting constituents simultaneously without consuming power or reducing gas.
However, the honeycomb monolith of the abovementioned “Electrochemical-Catalytic Converter” needs one half of the channels to be sealed to form the electrocatalytic tubes; this decreases the treating area, in comparison to the conventional honeycomb as automotive catalytic converter, and also increases the fabrication cost. Therefore, the prior art has room to be improved.